I recently made the mistake of getting a rebuilt 390 from Ford. After installing it in my truck with what I was told was an RV type cam and a brand new Holly 570 Street Avenger, I found out I had no power on the bottom end where I need it. What power I have is on the top end, not where I need it. My mechanic did a compression test and the pressure read between 95 and 100. Not very good. He also thinks there was too much cam for the motor. It also has vacuum at idle so he disconnected the vacuum advance and set the advance at about 15 deg. It has stock exhaust. Soooo. After all this effert what can I do to fix the problem short of taking it back out and rebuilding it right.

Thanks
Rocky

 

well without at least pulling the heads nothing. You can mill the heads, run the thin steel shim head gasket. And mill the intake. as an example:
"It is necessary to mill 0.030 in. off the head surface and use a 0.020-thinner-than-stock head gasket (C3AZ-6051-B) to bring the compression back up to the 428's original 10.7:1.
The intake manifold must also be milled for proper port alignment. 0.030 in. must be taken off the sides and 0.042 in. from the bottom"

from a 60's muscle article about adapting CJ stuff to 390's. so mill the heads, and run a thin head gasket will help. Also you might consider a cam change, or if you are using the adjustable rocker arms switch to the non adjustable's if your mechanic agree's because it'll make the cam slightly smaller, but the compression seems REALLY low

 

Rockyfast, I didn't think Ford offered reman FEs anymore, who built this engine anyway ? You mechanic is right, 95-100 seems too low. Keep in mind that big cams have lower cranking compression because of their overlap. Maybe a change to a smaller cam would help ? Is the cam in straight up or is it advanced or retarded ? An incorrectly timed cam can give low compresssion. Hooking the vacuum advance back up will also help low speed power, I like to see full manifold vacuum to the dizzy all the time. You could also have the heads milled if you want, you can take up to .060 off the decks safely, but don't you dare mill the intake ! An intake should never be milled. Mill the intake surface on the heads the same amount as the decks, and use a nice bead of RTV instead of end seals on the intake manifold and it will be fine. DF

 

I belive the cam is strait up. The guy that put in the cam used the stock timing set. I bought the reman. motor from a local Ford Dealer. I also have the stock cam but if I go to the trouble of changing I'll see what other options I have.

Thanks for your ideas.

Rocky

 

Most true RV cams are close to stock so I can't imagine an RV cam lowering compression by very much. You really should have gotten a cam card with the engine. I'd take it back and have them fix it, because that kind of compression is just plain wrong.

RV cams are supposed to be for towing and heavy loads, they might have used some cheap screwy cam and said it was an RV cam. Either way, I'd call the dealer because I'm guessing you paid quite a bit for that mill.

 

How much was that reman from Ford anyway?

 

The motor cost me about $1900. A good rebuid would have been about the same. The problem was time. I needed to get back on the road ASAP. I also had a 360 in it at the time. I wont go this route again. If I have to I'll rent a car while I wait on the machine shop.

By the way I'm redoing a 73 F250 w/ C6 Auto.

 

That doesn't really surprise me. Everyone I know who has purchased a "rebuilt" motor has had problems with it. Following Otto von Bismarck's classic advice ("Only fools learn from their mistakes; wise men learn from others' mistakes."), I decided to rebuild mine myself. It's going to take a lot more time (I told my wife to expect the garage to be occupied by my truck from September to April), but in the end I will know it was done right, and I'll have saved a few bucks, too.

 

I purchased a remanufactured 390 long block from my local Ford dealer in 1993 for my 71 f-100, and never had any trouble with it. It was rated 255 HP and cost $1325. But,just this week I tryed to get another one and was told the only 390 available was for a 75 and up. Problem is the HP is only rated at only 185,but the cost for a long block was $1420 & $300 core. I live on the west coast and the supplier for my local dealer is "Geniune Parts Distributers". They distribute only Ford authorized remanufactured parts. I have a catalog of theirs and when I called them they were much more helpful and knowledgable than my dealer was. They also said I could buy direct from them without going thru the dealer. The part # for the 390 long block is C8TZ 6V012 CRM. If you can live with 185 HP the price is very reasonable for a long block, and the good thing is ALL Ford dealers will honor the warranty.
Yvonne

 

The reason the '75-76 specification 390s have only 185 horse is largely due to the fact they have very low compression pistons in those years of truck engines. I would also suspect that the oiling issues are not addressed. If you look up engine rebuilders in the yellow pages I'm sure you will find somebody that can build an FE. If you ask your builder to use L2291F TRW pistons and a "801" Crane cam, 400 hp is within easy reach. What city are you in ? DF

 

Good point. After reading all the books, I wouldn't buy one in stock form. Just look at the oiling hole and the mismatch on the mains.

I've had good luck finding some of the older shops with older machinists or a race engine builder.

 

Very interesting string of postings here. I to am rebuilding a 1967 390 and have noticed many things that should be addressed during the rebuild that would not have been if I purchased a complete remaned engine.

I changed a few things on this rebuild like going from 2bbl to 4bbl performer intake, added a performer cam and springs. The heads were drilled for hardened valve seat inserts so I can run on no-lead gas. I also went with flat top pistons which I think might have raised my compression too high. I also painted the lifter valley and around the valve springs with Red Glyptal to speed oil return to the pan. Also added a windage try.

My point: I would rather rebuild then buy a remanufactured engine because I found some pretty bad stuff. I rebuilt the engine because of a wrist pin knock but after I started the rebuild I noticed that one rod and cap were machined way out of square so I replaced it but the engine ran for 70K miles like that. Next, the new center cam bearing was under size and the cam could not be installed. The answer here was to scrape the bearing, I didn't like doing that. Then all the oil holes in the mains did not line up with the holes in the bearings. I had to file out as much as half a hole diameter to get them to match up. Also, during the machining process I had the oil pick up hole to the main gallery drilled out to ½" like most books suggest.

So, I'm glad I rebuilt my own engine because I know it's much more reliable now.